docs: def cid(self):
          """The PubChem Compound Identifier (CID).
  
          .. note::
  
              When searching using a SMILES or InChI query that is not present in the PubChem Compound database, an
              automatically generated record may be returned that contains properties that have been calculated on the
              fly. These records will not have a CID property.
          """
          if 'id' in self.record and 'id' in self.record['id'] and 'cid' in self.record['id']['id']:
              return self.record['id']['id']['cid']